Final answer:
The ratio of illuminance over time from a lighting fixture is a physics concept related to light and optics, calculated using the illuminance formula. Luminous flux in lumens, not wattage, is the correct measure for comparing the brightness of lighting fixtures. This principle also helps in determining the distance of stars based on their apparent brightness.
Step-by-step explanation:
The ratio of illuminance produced by a lighting fixture at some specified point in time compared to the illuminance produced by the same fixture upon installation is a measure of the bulb's efficiency and light decay over time. This is a concept in physics, specifically in the study of light and optics. To calculate the illuminance at a distance from a light source, you can use the formula illuminance = P / (4πr²), where P is the luminous flux in lumens and r is the distance in meters from the source to the surface in question. For instance, a light bulb with a luminous flux of 942 lumens would have an illuminance of 33.321x on a surface 3.00 m away from the bulb.
When comparing the brightness of different light bulbs, it is important to look at the lumens value on the packaging rather than watts since lumens accurately represent how bright a light source will be perceived by the human eye. This concept also applies to understanding the apparent brightness of stars, as stars with the same luminosity will appear different in brightness based on their distance from the observer.